It may be known that the increasing miniaturization of portable electronic applications has brought about an intense, strong interest from those skilled in the art towards identifying new sources of electric energy and towards making equipment for exploiting them. All of this is to overcome the use of now conventional batteries, for example, lithium ion batteries.
It may be known that, amongst the new portable electric energy sources, micro fuel cells, hereafter referred to as microcells, in other words, those devices capable of obtaining electric energy from an appropriate fuel, for example through redox reactions, have been of great interest.
A known micro fuel cell is schematically illustrated in FIG. 1, wholly indicated with 1. In particular, the micro fuel cell illustrated uses a solid polymer electrolyte [Proton Exchange Membrane Fuel Cells]. Such a micro fuel cell 1 includes two electrodes, an anode A and a cathode C, separated by an electrolyte, which, instead of being a liquid, is solid and includes a thin polymeric membrane. The thin polymeric membrane allows the H+ protons to pass from the anode A to the cathode C (PEM or Proton Exchange Membrane).
In particular, the advantages of using a membrane electrode assemblies (MEAs) as illustrated in FIG. 1 suitably sandwiched between the anode A and the cathode C to make the micro fuel cell 1 may be known. The micro fuel cells are typically energy converters that, by exploiting the energy content of a chemical fuel, for example, through a redox reaction, allow electric energy to be reversibly produced. Reaction by-products are thus supplied, in particular heat and water. It may also be known that attention of researchers in this field has turned towards identifying fuels that when appropriately treated in respective micro cells, allow electric energy to be obtained easily and cleanly with increased yields.
Currently, hydrogen and methanol are the preferred fuels for treatment in micro cells, in particular, those using solid polymer electrolyte. The power density produced by such micro fuel cells, which is the main prerequisite in portable applications, is greatly influenced by the type of fuel used.
An energy density that can be obtained by a micro fuel cell supplied with hydrogen under the same conditions is greater by a few orders of magnitude than that obtained by an analogous micro cell supplied with methanol. Hydrogen is thus, the desired fuel to use for micro fuel cells for which an increase power density is desired, for example, for portable applications.
In particular, in a hydrogen micro cell 1, the anode A is supplied with hydrogen gas (pure) and then via a catalyst (usually platinum), is separated into protons and electrons. At this point, the protons migrate towards the cathode C through the polymeric MEA membrane, and the electrons, being unable to cross such a membrane, reach the cathode C passing through an external circuit (not illustrated), thus producing an electric current. Oxygen (which may be the oxygen contained in air) also arrives at the cathode C and recombines again with the help of a catalyst (again usually platinum), with the protons coming from the polymeric MEA membrane, and with the electrons coming from the external circuit, thus forming water.
However, to obtain sufficient amounts of electric energy from a hydrogen micro cell for satisfactory, long-lasting operation of a respective portable electronic device, in particular, sufficient amounts of energy to justify a gradual replacement of the batteries currently used as portable energy sources, it is desirable for the micro cell to have a substantial “reserve” of hydrogen available. For the aforementioned purpose, taking into account the techniques for producing hydrogen adopted up to now, the extremely reduced size of the electronic devices under consideration, and that of the micro fuel cells associated with the devices, the aforementioned may be satisfied by using small tanks (cylinders) in which the hydrogen is stored in gas state at very high pressures, or even liquefied at very low temperatures.
Known technical approaches for storing hydrogen include compressing hydrogen in gaseous phase under high pressure, for example 200-350 bar at a temperature of 20° C. It may be known to store hydrogen in liquid form at very low temperatures, for example equal to −253° C. for a pressure of one bar.
The operative conditions (temperature and pressure) for the storage of hydrogen in liquid and gas form carried out according to the prior art can be summarised in the following table:
TABLE 1TemperaturePressureStorage system(° C.)(bar)liquid H2−2531compressed H220200-350
In addition to the recognized danger of the different manipulations, it may be desirable to subject hydrogen to, in order to store it in small tanks in the aforementioned conditions, other drawbacks of the known techniques that include such manipulations that should be carried out between the production of the hydrogen and its transformation into electric energy, involving respective methodologies, apparatuses, and devices that are generally difficult to carry and control. Moreover, as far as the liquefaction of hydrogen is concerned, it may be known that it involves a total energy loss of about 30% since keeping the hydrogen in liquid form involves keeping it at a temperature of −253° C. Moreover, to keep hydrogen in liquid form it is desirable to use cryogenic containers that, as well as being expensive instruments, generally require a reduction of fuel losses by evaporation to a minimum.
For these reasons, the use of hydrogen as energy vehicle in portable commercial systems has not yet experienced the great, advantageous widespread use that its potential would make us think. In any case, at the moment, on the market there are no portable systems for producing electric power based upon micro fuel cells supplied with hydrogen.